This proposal addresses critical issues that will directly influence the treatment of two important gastrointestinal diseases: cystic fibrosis (CF) and secretory diarrhea. Both diseases target the small intestine and are linked by the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. Current information implicates up-regulation of CFTR in the pathogenesis of secretory diarrhea and down-regulation in CF pathogenesis. Nonetheless, the mechanisms that regulate CFTR are still poorly understood. Though cAMP and cGMP- dependent phosphorylation regulates CFTR, membrane traffic also regulates CFTR and appears to be important to the pathogenesis of both secretory diarrhea and CF. However, the physiologic role of this potentially important mechanism remains unknown. Studies testing the role of CFTR membrane traffic and its role in the regulation of anion secretion using cultured cells are conflicting. Furthermore, little has been done to understand the role of this important protein using natural endogenously CFTR-expressing tissues. This proposal will employ morphologic and biochemical cell biologic techniques in conjunction with electrophysiology and natural intestinal tissues to determine a role for membrane traffic in regulated CFTR and other potential alternate chloride channels and anion transport. Studies will primarily be performed in rat because of the similarity in intestinal distribution of CFTR to the human. These investigations will be complemented by studies in the normal and CF human intestine, and transgenic CFTR mouse intestinal tissues. Light and electron microscopic immunolocalzation techniques will identify the cell-specific sites of CFTR membrane traffic and chloride secretion. Functional biochemical techniques such biotinylation/immunoprecipitation will complement morphologic studied to investigate a role for membrane traffic. The studies and approaches outlined in this proposal are designed to achieve several goals: first to understand processes relevant to human physiology and disease pathogenesis, second to provide therapeutic avenues to correct defective traffic in CF and secretory diarrhea and third to use these skills to develop a career as an independent clinician scientist. This will be achieved by a comprehensive program to acquire both technical and intellectual skills from a cadre of distinguished and outstanding mentors and to draw on the scientific environments of various disciplines both in her home based institution and outside centers of excellence in related field of study.